Chemical based paint removers (also referred to as “paint strippers”) have enjoyed widespread commercial application due to their relative ease of use when compared to various physical scraping and/or sanding methods of paint removal. Many of these paint removers are solvent based, utilizing methylene chloride, methanol, butanol or other solvent components. While these solvents yield significant paint removal, they may also present potential health, safety and environmental concerns to both the user and the surrounding environment.
U.S. Pat. No. 2,507,983 discloses a paint stripper which contains methylene chloride and methylcellulose, which is a thickening agent used to increase the viscosity of the formulation. Methylene chloride is an effective low cost paint stripper characterized by high vapor pressure (400 mm Hg at 75° F.) which causes the methylene chloride to evaporate very rapidly. This high vapor pressure may lead to a vapor inhalation hazard. In addition, mehtylene chloride is a suspected carcinogen as well as a dermal irritant. A further concern of methylene chloride deals with possible ground water contamination when the residual stripper is removed from the substrate.
In an effort to reduce the health, safety and toxicity concerns related to methylene chloride based paint strippers, several formulations utilizing N-methyl-2-pyrrolidone (NMP) have been developed. NMP has been proposed as a substitute for chlorinated solvents because of its effectiveness, low toxicity, biodegradability and high flash point.
U.S. Pat. No. 5,049,300 discloses paint stripping compositions which include formic acid, NMP and ethyl-3-ethoxypropionate. This formulation acidifies the NMP with an organic or inorganic acid with a pH of 4.0 or less, with formic, sulfuric or phosphoric acid being preferred.
U.S. Pat. Nos. 4,812,255 and 4,749,510 also use formic acid as a component of the overall composition. However, each of the above formulations still presents a dermal safety hazard due to the low pH of the formic acid (pH=2.3) and other components.
U.S. Pat. No. 5,006,279 discloses a paint stripper composition which includes NMP and at least one mononuclear aromatic hydrocarbon.
Similarly, U.S. Pat. Nos. 4,120,810; 4,749,510 and 4,666,626 contain aromatic hydrocarbons within the paint stripper formulations.
These and other formulations, however, may still present potential health, safety and dermal hazards based on the absorption rate of the particular aromatic hydrocarbon or aromatic solvent used. In addition, many aromatic hydrocarbons are believed to be carcinogenic, pose environmental concerns and are troublesome regarding disposal of spent chemical.
U.S. Pat. No. 5,011,621 relates to mixtures of NMP, selected co-solvents (which may include aromatic hydrocarbons and terpenes such as d-limonene), as well as animal and/or vegetable oil, as a means to effectively remove paint from substrates. However, the presence of one or more of these natural components, such as tallows and fatty acids, may lead to the growth of microbiological organisms within the formulation, thereby decreasing the shelf life of the product. The presence of microbiological organisms could lead to altered product performance as well as a noxious and rancid odor, especially when the product is exposed to sunlight.
Thus, there remains a need in the industry to provide an effective paint removal composition which has a less than offensive odor, a long shelf life and is effective for the removal of most paints.